<div class="row">
  <div class="col-md-4">
    <select class="form-control" ng-model="vm.country" ng-options="country.label for country in vm.countries">
      <option value="">-- 请选择国家 --</option>
    </select>
  </div>
  <div class="col-md-4" ng-if="vm.country.provinces">
    <select class="form-control" ng-model="vm.province"
            ng-options="province.label for province in vm.country.provinces">
      <option value="">-- 请选择省份/州 --</option>
    </select>
  </div>
  <div class="col-md-4" ng-if="vm.province.cities">
    <select class="form-control" ng-model="vm.city" ng-options="city.label for city in vm.province.cities">
      <option value="">-- 请选择城市/县区 --</option>
    </select>
  </div>
</div>
<div>您选择的是：{{vm.country.label}} - {{vm.province.label}} - {{vm.city.label}}</div>
<div class="alert alert-info">
  这里使用ng-if指令来达到下一级有数据才显示下一级的效果
</div>

